Numerous commercial processes are carried out using a catalyst. This is especially true of various hydrocarbon conversion processes. These catalysts comprise one or more catalytic element deposited onto a relatively high surface area support. Further, the catalytic element or component can be evenly dispersed throughout the support, be dispersed on the surface of the support or present as a band below the surface.
The art also discloses catalysts containing an inert core or layer and an active outer layer or shell. For example, U.S. Pat. No. 3,145,183 discloses spheres having an impervious center and a porous shell. Although it is disclosed that the impervious center can be small, the overall diameter is ⅛″ or larger. It is stated that for smaller diameter spheres (less than ⅛″), uniformity is hard to control. U.S. Pat. No. 5,516,740 discloses a thin outer shell of catalytic material bonded to an inner core of catalytically inert material. The outer layer can have catalytic metals such as platinum dispersed on it. The '740 patent further discloses that this catalyst is used in an isomerization process. Finally, the outer layer material contains the catalytic metal prior to it being coated onto the inner core.
U.S. Pat. No. 4,077,912 and U.S. Pat. No. 4,255,253 disclose a catalyst having a base support having deposited thereon a layer of a catalytic metal oxide or a combination of a catalytic metal oxide and an oxide support. U.S. Pat. No. 5,935,889 discloses a catalyst which comprises a catalytically inert core material on which is deposited and bonded a thin shell of material containing active sites. Finally, U.S. Pat. No. 6,177,381 discloses a layered catalyst composition containing an inner core, an outer layer bonded to the inner core and where the outer layer has dispersed thereon a platinum group metal, a promoter metal and a modifier metal.
One problem associated with the layered compositions of the prior art is that the strength or attrition resistance was not sufficient for certain applications. Applicants have discovered that adding a fibrous component to the outer layer greatly increases its strength. The fibrous components can be either inorganic fibers such as silica or mullite fibers or organic fibers such as carbon fibers.